JPH11172378A - Multi-layer steel sheet with excellent pickling, corrosion resistance and workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a double layered steel sheet high in corrosion resistance in corrosive environments and excellent in pickling properties and workability. SOLUTION: In a double layer steel sheet in which components are different between the surface layer and the internal layer, the internal layer components are regulated to the ones contg., by weight, <=0.02% C, 0.01 to 3.0% Si, 0.1 to 3.0% Mn, 2.0 to 9.9% Cr, 0.002 to 7.0% Al, 5 to 500 ppm Ca+Mg, <=0.03% P, <=0.01% S, <=0.02%, N, and the balance Fe with inevitable impurities, and in the case the sheet thickness is defined as (t), as for the surface layer cocmponents in the part from 0.015 to 0.15 t per side from the surface and back faces, in addition to the above internal layer components, the % of the content of Al is made higher than that in the internal layer by 0.998 to 3.0%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel excellent in pickling and corrosion resistance, and more particularly, to a high-temperature wet corrosion environment such as an internal combustion engine exhaust system, a boiler exhaust system, a low-temperature heat exchanger, an incinerator floor, and the like. Bridges, pillars, building interior and exterior materials, roofing materials, fittings, kitchen components, various handrails, roof drains, atmospheric corrosion environments such as railway vehicles, various storage tanks, soil corrosion environments such as pillars, piles, sheet piles, can containers, various types Dew condensation corrosion environment (including freezing, humidification, and corrosive environment with mixed impressions) of containers, low-temperature heat exchangers, bathroom components, etc., water storage tanks, water supply pipes, hot water supply pipes, can containers, various containers, tableware, cooking equipment, bathtubs, Corrosion environment of tap water such as pools and vanities, canned containers, various containers, drinking water corrosion environment of tableware, cooking equipment, etc., concrete corrosion environment of various reinforced structures, pillars, etc., ships, bridges, piles, sheet piles, oceans For seawater corrosive environments such as structures, In the food environment, and excellent corrosion resistance,
The present invention relates to a multilayer steel sheet having good pickling properties and good workability.

[0002]

2. Description of the Related Art Steel plates used in corrosive environments such as high-temperature wet corrosive environment, dew condensation corrosive environment, atmospheric corrosive environment, tap water corrosive environment, soil corrosive environment, concrete corrosive environment, sea water corrosive environment, drinking water corrosive environment, etc. Often, some anti-corrosion measures are used together. In recent years, the use of Cr-containing steel and stainless steel for the purpose of improving the corrosion resistance of steel substrates has been increasing from the viewpoint of improving reliability, simplifying manufacturing and construction processes, maintaining maintenance, and saving resources. I have. However, in the conventional technology, the improvement in corrosion resistance leads to an increase in material cost, and is often not a practical measure from the viewpoint of economy. Further, the improvement of the corrosion resistance may cause a secondary problem such as a decrease in workability of the material.

[0003] For example, in the exhaust system of an internal combustion engine mainly for automobiles, steel in which ordinary steel is subjected to aluminum plating or zinc plating has been used in order to suppress corrosion from the inside or outside. Since the exhaust system was equipped with a catalyst etc. for the purpose of purifying exhaust gas to suppress environmental pollution, such a plated steel material did not have sufficient corrosion resistance, and contained 5-10% Cr for the purpose of improving the corrosion resistance of the steel base. Steels have been proposed in JP-A-63-143240 and JP-A-63-143241. However, along with the extension of the service period and the warranty period of vehicles in recent years, high-grade stainless steel containing more than about 18% of Cr or further adding Mo has been increasingly used. However, even such a high-grade stainless steel does not always have sufficient corrosion resistance such that pitting-like local corrosion may occur. In addition, these high-grade stainless steels contain a large amount of Cr and Mo, so their workability is poor, and in order to process them into complex shapes such as exhaust system members, there are extremely difficult manufacturing processes.
There is a drawback that the processing cost becomes high because the manufacturing process becomes extremely complicated. Or it may not be applicable depending on the shape. Also, the material cost is high.

As can be seen from the above examples, in general, steel containing a certain amount of Cr is susceptible to local corrosion when the corrosive environment becomes severe. In order to improve the resistance to corrosion, it is necessary to further improve the resistance to corrosion by using Cr or Mo. Increasing the content of was a very common technical measure.

[0005] In addition, corrosion-resistant steel often requires a great increase in load at the time of manufacture in exchange for improvement in corrosion resistance. That is, in order to obtain a corrosion-resistant material, it is well known that the addition of a corrosion-resistance improving element such as Cr, Cu, and Mo, which is conventionally generally used, greatly reduces the pickling property. Improving pickling properties is often an important issue from an economic viewpoint. A steel sheet having excellent corrosion resistance to which Cr, Cu, and Mo are added is excellent in corrosion resistance, and at the same time, is regarded as an acid-fast-washing steel in terms of pickling properties, similarly to conventional corrosion-resistant materials. Conventionally, in the manufacturing process of hard-to-pick steel, improvement of the deske efficiency by strengthening or changing the pickling solution, using electrolysis, using physical deske such as shot blasting or grinding, or combining these means Countermeasures were very common. However, these pickling-improving means involve a great deal of equipment investment and an increase in process load in taking measures, resulting in an increase in steel manufacturing costs.

In recent years, Japanese Patent Application Laid-Open Nos. Hei 5-79791 and Hei 6-17
No. 9949, JP-A-6-179950, JP-A-6-179951, JP-A-6-212256, JP-A-6-212257,
Japanese Patent Application Laid-Open No. 7-3388 proposes a steel in which Al is added to Cr for the purpose of improving corrosion resistance or improving corrosion resistance and workability. These steels are recognized to be effective to some extent in improving corrosion resistance or corrosion resistance and workability. However, as with conventional corrosion-resistant materials, they are regarded as difficult to pickle, as in conventional corrosion-resistant materials. At present, it has not been resolved.

Japanese Patent Application No. 9-1267 discloses a technique for achieving compatibility between pickling, corrosion resistance and workability.
At present, it has not been possible to avoid a phenomenon in which workability is reduced with an increase in the amount of l added.

[0008]

SUMMARY OF THE INVENTION In view of these circumstances, the present invention has been developed in consideration of the high-temperature wet corrosion environment, condensation corrosion environment, atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, seawater corrosion environment, beverage It is an object of the present invention to provide a low-cost multi-layer steel sheet having high corrosion resistance in a corrosive environment such as a water-corrosive environment and excellent in pickling and workability.

[0009]

Means for Solving the Problems In order to achieve the above objects, the present inventors have developed a high-temperature wet corrosion environment, a dew condensation corrosion environment, an atmospheric corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion environment, a seawater corrosion environment. In order to develop steel having excellent corrosion resistance in corrosive environments such as the environment and drinking water corrosive environment, studies were conducted from various viewpoints. First, as a result of various investigations on means for improving the corrosion resistance in the above-mentioned nuclear corrosion environment at the same time as excellent pickling properties, a steel containing 2 to 9.9% of Cr was added with 1% of Al.
Steel with 10% to 10% and Ca + Mg added at 5 to 500ppm has excellent pickling properties, and also shows excellent corrosion resistance in many corrosive environments described above. Mechanism of the effect of simultaneous addition of Ca and Mg There are many unclear points, but it has been found that under conditions where both coexist, excellent pickling properties and corrosion resistance that deviate from conventional knowledge are simultaneously achieved.

However, since the phenomenon that the workability of steel gradually decreases when the amount of Al added increases is inevitable, excellent pickling properties of the surface, corrosion resistance in various corrosive environments and good workability are required. 1] In a multilayer steel sheet having different components in the surface layer and the inner layer, as an inner layer component, C:
0.02% or less, Si: 0.01% to 3.0%, Mn:
0.1-3.0%, Cr: 2.0-9.9%, Al:
0.002 to 7.0%, Ca + Mg: 5 to 500 pp
m and P are 0.03% or less, S is 0.01% or less, N is 0.02% or less, and the balance: Fe and unavoidable impurities are contained. .01
As a surface layer component in a portion of 5 t to 0.15 t, in addition to the above-mentioned inner layer component, Al content% is 0.998 to 3.0 from the inner layer.
It has been found that this can be achieved at the same time by providing a multi-layered steel sheet having an excellent pickling property, corrosion resistance, and workability, which is increased in%.

Further, the present inventors have continued their studies as a better steel, and as a result, the above-mentioned steels were found to contain Cu, Mo, Sb, Ni,
When W is added alone or in combination, excellent corrosion resistance can be obtained without impairing excellent pickling properties,
When C and N are reduced, it is effective in improving corrosion resistance and workability without impairing excellent pickling properties, Si and Mn are appropriate as deoxidizing and strengthening elements, and C and N are reduced. It was found that when Nb, V, Ti, Zr, Ta, and Hf were added so as to satisfy specific conditions, it was effective in improving corrosion resistance and workability without impairing excellent pickling properties. Was.

The present invention has been made on the basis of the above findings. [Claim 2] In a multi-layer steel sheet having different components in the surface layer and the inner layer, as an inner layer component, in addition to the component described in claim 1, Further, by weight%, Cu: 0.05 to
5.0%, Mo: 0.05 to 3.0%, Sb: 0.01
0.5%, Ni: 0.01-6.0%, W: 0.05
３3.0%, one or more of the following, and the balance: F
e and unavoidable impurities, and assuming that the plate thickness is t, in addition to the above-mentioned inner layer component, Al content% is 0.1% from the inner layer as a surface layer component of 0.015 t to 0.15 t per side from the front and back surfaces. By making it a multi-layer steel sheet with 998 to 3.0% higher and excellent in pickling, corrosion resistance and workability, it is effective in improving workability without impairing excellent pickling and corrosion resistance. I found it.

[0013] Further, in the above invention, [Claim 3] In the multi-layer steel sheet having different components in the surface layer and the inner layer, as an inner layer component, in addition to the component according to the first or second aspect, furthermore, , Rare earth element: 0.001-0.
1%, and the balance: Fe and unavoidable impurities, and when the sheet thickness is t, 0.01 per side from the front and back surfaces.
As a surface layer component in a portion of 5 t to 0.15 t, in addition to the above-mentioned inner layer component, Al content% is 0.998 to 3.0 from the inner layer.
By making the steel sheet multi-layer steel excellent in pickling, corrosion resistance and workability, the heat pipe workability and corrosion resistance can be improved.

[0014] [Claim 4] In a multi-layer steel sheet having different components in the surface layer and the inner layer, in addition to the component described in the first, second or third aspect as an inner layer component, the composition further comprises Nb in weight%. , V, Ti, Zr, Ta, and Hf, wherein one or more elements selected from a total of 0.01 to 1.0% are contained, and the following formula is satisfied. The balance: Fe and unavoidable impurities are contained, and assuming that the plate thickness is t, 0.0 per side from the front and back surfaces.
As the surface layer component of the portion of 15 t to 0.15 t, in addition to the above-mentioned inner layer component, Al content% is 0.998 to 3.
Further improvement in workability is achieved by making the steel sheet multiplied by 0% and excellent in pickling, corrosion resistance and workability.

## EQU2 ## Nb / 93 + V / 51 + Ti / 48 + Zr / 9
1 + Ta / 181 + Hf / 179−0.8 × ΔC / 12
+ N / 14｝ ≧ 0

That is, the invention of the present application is that Al is indispensable for exhibiting excellent properties in pickling and corrosion resistance. The parts that require properties and corrosion resistance are made with a focus on the fact that they are exclusively surfaces. In the inner layer of the multi-layer steel sheet, the workability is improved by limiting the addition amount of Al and making it as small as possible.
By increasing the amount of 1 added to the inner layer of 0.998 to 3.0%, the necessary amount of Al is secured, and the pickling property and the corrosion resistance are improved. Thereby, pickling property, corrosion resistance and workability can be achieved at the same time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the range of each component in the present invention will be described below. Si: It is effective to add Si as a deoxidizing agent and a strengthening element to steel containing 2% or more of Cr, but if the content is less than 0.01%, the deoxidizing effect is not sufficient, and exceeds 3.0%. If contained, the effect is saturated and, on the contrary, the acid washability and processability are reduced, so the content range is limited to 0.01% or more and 3.0% or less. M
n: Mn must contain at least 0.1% of steel as a deoxidizing agent, but if it exceeds 3.0%, the effect is no longer saturated, but if Mn is excessively contained, it will be processed. Therefore, the upper limit of the content is set to 3.0% because the property is lowered. Cr: Cr is
In order to ensure corrosion resistance, it is necessary to contain 2% or more. However, if the content exceeds 9.9%, not only does the cost increase, but also the workability decreases, so the upper limit content is 9.9%. Al: Al is used to ensure corrosion resistance in the present invention.
It is an important element along with Ca + Mg and Cr.

If the content of Al is less than 0.002%, deoxidation becomes insufficient and blowholes occur in the steel, impairing the cleanliness of the steel sheet and causing cracking during pressing.
The lower limit of the inner layer is set to 02%, and the upper limit of the inner layer is set to 7.0% since the workability is remarkably deteriorated if it exceeds 7.0%. On the other hand, in order to ensure corrosion resistance and pickling properties that suppress the occurrence of pitting corrosion as properties of the steel sheet surface,
Since the Al content is required to be 1% or more in the surface layer of 0.015 t to 0.15 t, the lower limit of Al of the inner layer is 0.002%.
Therefore, the lower limit of the amount of Al added to the surface layer is 0.998.
%. In addition, in the production of a multi-layer steel sheet, since the maximum addition of Al to the inner layer is 3.0%, the upper limit of the amount of Al added to the surface layer is set to 3.0%.

In the present invention, Al: 0.998-
The thickness of the surface layer to which 3.0% is added is the total thickness t per one side.
0.015 to 0.15 t. The reason is that when the surface thickness is less than 0.015 t per side, Al: 0.99
Since the thickness is not sufficient to obtain the corrosion resistance and pickling effect of suppressing the occurrence of pitting corrosion by adding 8 to 3.0%, the addition of 0. 3% is not sufficient.
015t is the lower limit.
Since the ratio of the thickness of the surface layer containing 998 to 3.0% higher becomes higher and the workability of the entire steel sheet deteriorates, the upper limit is set to 0.15.
Let it be t.

Ca + Mg: Ca and Mg consist of 2% or more of Cr and 1% of Al.
% Or more of steel contained in the surface layer is the most important element along with Al to secure acid resistance as well as corrosion resistance. At present, there are many unclear points about the mechanism, but the sum of the two
If it is less than 5 ppm, good pickling properties cannot be obtained. On the other hand, from the viewpoint of corrosion resistance, when the total is 10 ppm or more, the corrosion resistance is further improved,
With the increase of the total amount, the improvement of the corrosion resistance is recognized. However, it is clear that the addition of more than 500 ppm not only saturates the corrosion resistance improvement effect but also lowers the pickling property, and the content of Ca + Mg is 5 ppm. It is limited to not less than 500 ppm. C, N: C and N reduce the workability of the steel sheet, and C forms carbides with Cr to reduce the corrosion resistance: and because N decreases the toughness, the C and N contents are smaller. It is desirable that the upper limit of the content is 0.02%. It is preferable that each of them is as small as possible. P: If P is present in a large amount, the toughness is reduced. Therefore, it is desirable that P is small, and the upper limit content is 0.03%. It is preferable to minimize the content that is inevitably mixed. S: Since the presence of a large amount of S lowers the pitting corrosion resistance, a smaller amount is desirable, and the upper limit content is 0.01%. As with P, it is preferable that the inevitable mixing amount of S be as small as possible.

The steel of the present invention has the above-mentioned component composition as a basic component, but in order to further improve the corrosion resistance, it is necessary to further improve the corrosion resistance.
One or more of Cu, Mo, Sb, Ni, and W are contained. Cu: Cu contains 2% or more of Cr, 1% or more of Al,
Addition of 0.05% or more to steel containing 5 ppm to 500 ppm of Ca + Mg has the effect of improving the resistance to general corrosion without impairing excellent pickling properties. However, adding more than 5.0% decreases the pickling properties. Therefore, it is set to 0.05 to 5.0%. Mo: Mo contains 2% or more of Cr and 1% or more of Al,
Addition of 0.05% or more to steel containing 5ppm to 500ppm of Ca + Mg has the effect of suppressing pitting corrosion and growth without impairing excellent pickling properties. Not only saturates but also reduces workability.
05 to 3.0%. Sb: Sb also contains Cr 2% or more, Al 1% or more,
When 0.01% or more is added to steel containing 5 ppm to 500 ppm of Ca + Mg, the effect of improving resistance to pitting corrosion and general corrosion can be observed without impairing excellent pickling properties, but 0.5%
If added in excess of, the pickling properties and hot workability are reduced, so the content is made 0.01 to 0.5%. Ni: Ni contains 2% or more of Cr and 1% or more of Al,
When 0.01% or more is added to steel containing 5ppm to 500ppm of Ca + Mg, the effect of suppressing pitting corrosion is recognized without impairing excellent pickling properties, but the effect is only saturated when added over 6.0%. Or lowers hot workability, 0.01-6.0%
And W: W contains 2% or more of Cr and 1% or more of Al,
When added to steel containing 5 ppm to 500 ppm of Ca + Mg and added in an amount of 0.05% or more, the effect of suppressing the occurrence of pitting corrosion and growth is notably impaired without impairing excellent pickling properties, but exceeding 3.0% Even if added, the effect is not only saturated, but also the pickling property and the workability are reduced.

In the steel of the present invention, a rare earth element (REM) is selectively contained as an element for further improving the corrosion resistance. Rare earth element (REM): Rare earth element contains 2% or more of Cr, 1% or more of Al, and is added to steel containing 5ppm to 500ppm of Ca + Mg, without impairing excellent pickling performance. , Is an element that is effective in improving hot workability and pitting corrosion resistance, but the effect is not sufficient if the addition amount is less than 0.001%, and if added over 0.1%, coarse non-metallic inclusions Since the material is formed and conversely deteriorates hot workability and pitting resistance, the content is made 0.001 to 0.1%. In the present invention, the rare earth elements refer to elements having atomic numbers 57 to 71 and 89 to 103 and Y.

In the steel composed of the above-mentioned steel components and having excellent pickling and corrosion resistance: one or two of Nb, V, Ti, Zr, Ta, and Hf are required if workability is also required. The above is included. Nb, V, Ti, Zr, Ta, Hf: Nb, V, Ti, Zr, Ta, Hf are:
Contains 2% or more of Cr, 1% or more of Al, and 5p of Ca + Mg
By fixing C and N in the high Cr steel as carbides without impairing the excellent pickling properties of the basic component steel containing pm to 500 ppm, a remarkable effect on improvement of corrosion resistance and workability is recognized. Each of these elements can be added alone or two or more elements can be added in combination. However, if the total amount of the single or combined additions is less than 0.01%, there is no effect. If added in excess of%, the cost will be increased and roll flaws will be caused, so the total amount is made 0.01 to 0.5%. In addition, in order to effectively improve the workability, the total amount of Nb, V, Ti, Zr, Ta, and Hf needs to satisfy the following expression.

## EQU3 ## Nb / 93 + V / 51 + Ti / 48 + Zr / 9
1 + Ta / 181 + Hf / 179−0.8 × ΔC / 12
+ N / 14｝ ≧ 0 If the above expression is not satisfied, the immobilization of C and N becomes insufficient, and it becomes difficult to obtain the effect of improving workability.

In the method for producing a multilayer steel sheet according to the present invention, for example, the position of a molten steel injection nozzle and the position of a static magnetic field in a mold for continuous casting are accurately arranged, and Al is placed from above the mold during casting.
A method of adding a surface element with a wire or the like containing an alloy is preferable. Also, this wire is power,
Melt addition may be performed by auxiliary heating such as gas heating.

When the multi-layer steel sheet of the present invention is used, for example, after being manufactured as a multi-layer steel ingot, it is subjected to hot rolling, forging, cold rolling,
It may be formed into an arbitrary shape such as a steel plate, a bar, a steel bar, a sheet pile, or the like by drawing, formed into a predetermined shape by a press or the like, and further processed and welded to produce a product. First, it may be used for the product by secondary processing and welding etc. after making it into the shape of a steel pipe, etc. It is possible to select the optimum product manufacturing process including other processes due to cost and restrictions of existing manufacturing equipment etc. The steel of the present invention can be manufactured regardless of which manufacturing process is selected.

The steel of the present invention has an alloy having an appropriate composition on the surface of Al.
Alternatively, an Al alloy further containing a necessary element is deposited by a method such as a plating method or a cladding method, and the element is diffused by an appropriate treatment such as a heat treatment, so that a steel material having a surface having a chemical composition described in the claims may be used. .

The steel of the present invention is a composite of these corrosive environments such as a high temperature wet corrosive environment, a dew condensation corrosive environment, an atmospheric corrosive environment, a tap water corrosive environment, a soil corrosive environment, a concrete corrosive environment, a seawater corrosive environment, a drinking water corrosive environment and the like. It can be applied to various corrosive environments.

[0027]

Embodiments of the present invention will be described below. 1) Evaluation of pickling properties The surface layer components shown in Tables 1 to 6 and the multi-layered steel having the inner layer components were melted and formed into a steel ingot by a normal steel ingot manufacturing process, followed by hot rolling, and a sheet thickness of 2.5 mm sample. Next, test pieces having a width of 50 mm and a length of 70 mm were collected from these steel sheets and subjected to a pickling test. In the pickling test, a test piece was immersed in a 5% hydrochloric acid aqueous solution heated to 80 ° C. to remove the surface scale. The test results are shown in Tables 1 to 6. In the results of the pickling test, ◎ indicates that the pickling was completed within 20 seconds, and ○ indicates 40.
The pickling was completed within seconds, the 酸 indicates that the pickling was completed within 60 seconds, and the X indicates that the pickling was not completed even with a treatment time of 120 seconds or more. As is clear from Tables 1 to 6, it is understood that the steel of the present invention shows good pickling properties, whereas the comparative steel is inferior in pickling properties.

2) Evaluation of workability Workability was evaluated by performing a cylindrical drawing test. Aperture ratio 2.
The sample which did not crack even at 0 was ◎, the crack did not occur at a drawing ratio of 1.8, but the product which cracked at a drawing ratio of 2.0 was ○, and no crack occurred at a drawing ratio of 1.6. When the ratio was 1.8, the material that cracked was rated as Δ, and when the drawing ratio was 1.6, the material that cracked was rated X. The test results are shown in Tables 1 to 6. Tables 1 to 6 also show the workability evaluation results of the single-layer steel sheet having a surface layer component. It can be seen that the workability has been improved by forming a plurality of layers and reducing the amount of Al in the inner layer.

3) Evaluation of corrosion resistance A multi-layer steel having surface layer components and inner layer components shown in Tables 1 to 6 is melted and formed into a steel plate having a thickness of 1 mm by a normal steel plate manufacturing process such as hot rolling or cold rolling. Annealing was performed at 850 ° C., and test pieces having a width of 50 mm and a length of 70 mm were collected from these steel sheets and subjected to various corrosion tests described below.

The high-temperature wet corrosion test was carried out with a sulfate ion of 100 ppm,
The test piece is immersed in 50 cm ^{3 of} an aqueous solution containing 100 ppm of chloride ion and 500 ppm of bicarbonate ion in the form of ammonium salt, and the test solution is completely evaporated and volatilized by keeping the test container in an atmosphere at 130 ° C together The test was repeated 50 times. The test results are shown in Tables 1 to 6. In the results of the corrosion test, ◎ indicates that the maximum corrosion depth is less than 0.20 mm, ○ indicates that the depth is less than 0.3 mm,
△ indicates less than 0.4 mm, and × indicates 0.4 mm or more. As is apparent from Tables 1 to 6, symbols 1 to 72 in Tables 1 to 6 of the steel of the present invention show good corrosion resistance even in a very severe corrosive environment such as high-temperature wetting containing chloride. On the other hand, the symbols A to Z in Tables 1 to 6, which are comparative steels, are inferior in corrosion resistance, or are inferior in pickling even if a certain degree of corrosion resistance is obtained.

The tap water environmental corrosion test was a test in which a test piece was immersed in tap water and kept in an atmosphere at 40 ° C. for 3 months. The test results are shown in Tables 1 to 6. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, Δ indicates that the rusting area ratio was less than 10%, and × indicates that
% Respectively. As is clear from Tables 1 to 6, symbols 1 to 6 in Tables 1 to 6 which are the steels of the present invention.
72 shows good corrosion resistance in a tap water corrosive environment, whereas symbols A to Z in Tables 1 to 6, which are comparative steels, have poor corrosion resistance or are pickled even if some corrosion resistance is obtained. It turns out that it is inferior in nature.

The seawater environment corrosion test was a test in which a test piece was exposed to a shore splash zone for 12 months. The test results are shown in Tables 1 to 6. In the corrosion test results, ◎ indicates that the corrosion depth was less than 0.05 mm, ○ indicates less than 0.1 mm, Δ indicates less than 0.3 mm, and × indicates
It is 0.3mm or more respectively. As is clear from Tables 1 to 6, symbols 1 to 72 in Tables 1 to 6 of the present invention steel show good corrosion resistance in a seawater corrosive environment, whereas Comparative Steel 1 It can be seen that symbols A to Z in Tables 6 to 6 are inferior in corrosion resistance, or inferior in pickling even if a certain degree of corrosion resistance is obtained.

In the dew condensation corrosion test, it is necessary to maintain the humidity of 90% and the environment of 25 ° C. for 4 hours after maintaining the environment at −20 ° C. for 2 hours.
The test was repeated twice. The test results are shown in Tables 1 to 6. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, Δ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more. . As is clear from Tables 1 to 6, the symbols 1 to 72 in Tables 1 to 6 of the steel of the present invention show good corrosion resistance in a dew-condensation corrosion environment, whereas the steels of Comparative Example 1 have good corrosion resistance. It can be seen that symbols A to Z in Tables 6 to 6 are inferior in corrosion resistance, or inferior in pickling even if a certain degree of corrosion resistance is obtained.

The atmospheric corrosion test was a test in which a test piece was exposed to a position about 500 m from the coast for about 700 days. Test results first
Tables 6 to 6 also show the results. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, △ indicates that the rusting area rate was less than 10%, and X indicates that the rusting area ratio was 10% or more. As is clear from Tables 1 to 6, symbols 1 to 72 in Tables 1 to 6 of the steel of the present invention show good corrosion resistance in an atmospheric corrosion environment. ~ 6
It can be seen that the symbols A to Z in the table are inferior in corrosion resistance, or inferior in pickling even if a certain degree of corrosion resistance is obtained.

In the soil corrosion test, the water content was 15% and the specific resistance was 500.
A test piece was embedded in sand adjusted to the content of sodium chloride in Ω · cm, and left at 25 ° C. for about 700 days. The test results are shown in Tables 1 to 6. In the corrosion test results, ◎ indicates that the maximum corrosion depth is less than 0.05 mm, ○ indicates that the corrosion depth is less than 0.1 mm,
△ indicates less than 0.5 mm, and × indicates more than 0.5 mm. As is clear from Tables 1 to 6, the symbols 1 to 72 in Tables 1 to 6 of the steel of the present invention show good corrosion resistance in a soil corrosion environment, whereas the comparative steels 1 to 72 have good corrosion resistance. Symbols A to Z in Tables 1 to 6 indicate that the corrosion resistance is inferior to the corrosion resistance, or that the pickling property is inferior even if a certain degree of corrosion resistance is obtained.

The concrete corrosion test is conducted by embedding a test piece in Portland cement kneaded with sea sand containing chloride to form a sample, solidifying the sample, immersing the sample in artificial seawater to half its temperature, at 40 ° C. The test was to be left in the environment for about 700 days. The test results are shown in Tables 1 to 6. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, and △ indicates that the rusting area rate was 10%.
%, And X indicates 10% or more, respectively. As is clear from Tables 1 to 6, the steels of the present invention, Nos. 1 to 6
Symbols 1 to 72 in the table show good corrosion resistance in a corrosive environment in concrete, whereas symbols A to Z in Tables 1 to 6, which are comparative steels, have poor corrosion resistance or have some degree of corrosion resistance. It can be seen that even if it is obtained, it is inferior in pickling properties.

In the drinking water environmental corrosion test, the pH was adjusted to 2.8 using sodium hydroxide, degassed by passing high-purity nitrogen gas, and maintained at 27 ° C., (a) a 0.5% phosphoric acid solution, (b) 0.5
The test piece was immersed for 20 days in a 850CC solution such as a 0.5% citric acid solution, (C) a 0.5% citric acid-0.5% sodium chloride solution, and the amount of iron ions eluted in the solution was analyzed. The test results are shown in Tables 1 to 6. In the results of the corrosion test, ◎ indicates that the elution amount of iron ions into the solution was 1 ppm or less, △ indicates less than 3 ppm,
○ indicates less than 5 ppm, and X indicates 5 ppm or more. As is clear from Tables 1 to 6, the symbols 1 to 72 in Tables 1 to 6 of the steel of the present invention show good corrosion resistance in a drinking water corrosive environment, while the comparative steels The symbols A to Z in Tables 1 to 6 are inferior in corrosion resistance, or are inferior in pickling even if a certain degree of corrosion resistance is obtained.

That is, the symbols 1 to 72 in Tables 1 to 6, which are the steels of the present invention, are a high temperature wet corrosion environment, a dew condensation corrosion environment, an atmospheric corrosion environment, a tap water corrosion environment, a soil corrosion environment, a concrete corrosion environment, a sea water corrosion environment. In contrast, while showing good corrosion resistance in various corrosive environments such as drinking water corrosive environments, the symbols A to Z in Tables 1 to 6, which are comparative steels, are inferior in corrosion resistance or have some degree of corrosion resistance. It can be seen that the pickling properties are poor even when the cleaning is performed.

As is clear from Tables 1 to 6, symbols 1-36 and 37 to 72 in Tables 1 to 6 of the steel of the present invention show good pickling properties, high-temperature wet corrosion environment, dew condensation corrosion. It shows good corrosion resistance in various corrosive environments such as environment, atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, seawater corrosion environment, drinking water corrosion environment, etc. The symbols A to M in Tables 1 to 6, which are comparative steels,
It turns out that NZ cannot simultaneously achieve pickling, corrosion resistance, and workability.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

[Table 5]

[0045]

[Table 6]

[0046]

According to the present invention, it is possible to provide a multi-layer steel sheet having high corrosion resistance in a corrosive environment, and excellent in pickling and workability, and the effect is extremely large.

Claims (4)

[Claims] 1. In a multilayer steel sheet having different components in the surface layer and the inner layer, C: 0.02 by weight% as an inner layer component.
% Or less, Si: 0.01% to 3.0%, Mn: 0.1 to
3.0%, Cr: 2.0 to 9.9%, Al: 0.002
To 7.0%, Ca + Mg: 5 to 500 ppm, and P to 0.
03% or less, S is 0.01% or less, N is 0.02% or less, the balance: Fe and unavoidable impurities are contained, and the plate thickness is t
Then, from the front and back sides, 0.015 t to 0.1 per side
As a surface layer component of the portion of 5t, in addition to the inner layer component,
Al content% is 0.998-3.0% higher than the inner layer,
Multi-layer steel sheet with excellent pickling, corrosion resistance and workability. 2. In a double-layered steel sheet having different components in the surface layer and the inner layer, as an inner layer component, in addition to the component of claim 1, Cu: 0.05 to 5.0% by weight%;
Mo: 0.05 to 3.0%, Sb: 0.01 to 0.5
%, Ni: 0.01 to 6.0%, W: 0.05 to 3.0%
%, One or two or more, and the balance: Fe and unavoidable impurities, and assuming that the plate thickness is t, as a surface layer component of a portion of 0.015 t to 0.15 t per surface from the front and back surfaces, A multi-layer steel sheet excellent in pickling properties, corrosion resistance, and workability, in which the content of Al is 0.998 to 3.0% higher than that of the inner layer in addition to the components of the inner layer. 3. The multi-layer steel sheet having different components in the surface layer and the inner layer, as an inner layer component.
In addition to the components described in the above, further, in weight percent, rare earth elements:
0.001 to 0.1%, and the balance: Fe and unavoidable impurities, and assuming that the plate thickness is t, as a surface layer component of a portion of 0.015 t to 0.15 t per surface from the front and back surfaces, A multi-layer steel sheet excellent in pickling properties, corrosion resistance, and workability, in which the content of Al is 0.998 to 3.0% higher than that of the inner layer in addition to the components of the inner layer. 4. A multi-layered steel sheet having different components in the surface layer and the inner layer, in addition to the component according to claim 1, 2 or 3 as an inner layer component, further comprising Nb,
One, two or more elements selected from V, Ti, Zr, Ta and Hf in a total content of 0.01 to 1.0.
%, And the following formula is satisfied. The balance: Fe and unavoidable impurities are contained, and assuming that the plate thickness is t, a portion of 0.015 t to 0.15 t per one surface from the front and back surfaces. A multi-layer steel sheet excellent in pickling properties, corrosion resistance, and workability, in which the content of Al is 0.998 to 3.0% higher than that of the inner layer in addition to the inner layer component as a surface layer component. ## EQU1 ## Nb / 93 + V / 51 + Ti / 48 + Zr / 9
1 + Ta / 181 + Hf / 179−0.8 × ΔC / 12
+ N / 14｝ ≧ 0